On 09/01/11 18:31, Wayne Stallwood wrote:
On 09/01/11 09:07, nev young wrote:
I suspect it is caused by a (static?) discharge as I have been able to measure a potential of about 150 volts between the two devices (laptop & TV set) although there is no current available to do any (much) damage.
I just fall back on the old hardware adage of "don't plug or unplug under power".
That isn't static, it sounds like a ground level mismatch between the two devices.
If your TV set has an earth pin connection then I would get the set PAT tested or have the earth bonding in whatever mains socket you have it plugged into checked out.
Laptops are a bit of a funny beast when it comes to Ground as they tend not to have a ground connection bonded to mains earth through the PSU so there is potential (lol) for a ground mismatch when compared against another item. But a 150v PD between the two would suggest to me that one of them is faulty or there is something very wrong with your mains wiring.
TVs do not have an earth connection. This is a standard for such devices and has been for over 40 years.
There should be no connection between earth and the output of a laptop power brick.
Many devices are not earthed by design. At least that was the case when I was an electrical engineer. Things may have changed since I became a software engineer.
The PD of about 150v is very high impedance, well over 100MΩ, and is quite normal for such devices. You need a *special* voltmeter to read it. It is not normally a problem as it leaks away eg. via moisture in the atmosphere, but sometimes it can bite you.
The reason for it being about 150v is it is (√2/2)*(peak mains volts).